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Lithium-ion Batteries Part 5

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Tham khảo tài liệu 'lithium-ion batteries part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Thermo-chemical process associated with lithium cobalt oxide cathode in lithium ion batteries 49 decomposition of LixCoC 2 into LiCoO2 CO3O4 and oxygen. The reduction of CO3O4 into lower cobalt oxide or to cobalt depends on the extent of electrolyte solvent present in the sample. The liberated oxygen oxidizes the carbonaceous materials releasing carbon dioxide and energy. In MacNeil Dahn 2001 the authors analyzed the XRD pattern of Li0.5CoO2 sample heated with and without organic solvent using ARC and demonstrated that the former one even at lower temperature 275 C not only produces LiCoO2 and CosO4 but also shows the presence of LixCo 1_x O. Since the amount of lithium Li is very small the authors refer LixCo 1-x O as CoO. Fig. 8 shows that the highly charged electrode materials of 4.20 and 4.35V cells to undergo pronounced weight loss compared to electrode materials of cells charged to lower voltage cells 3.85 and 3.95V . The highly charged material with low value of lithium could behave well like an oxidizing agent towards the electrolyte which may lead to the formation of less quantity of LiCoO2 and Co3O4 but with larger proportion of CoO. 105 85 ------i-----i----i-----i----1-----1----1-----1-----1- 5Ũ 100 150 200 250 30c 5ỖO 400 450 500 550 BOO Temperature C Fig. 8. TGA curves for the different cathode materials veluchamy et al. 2008 . 6.1.7 Differential Scanning calorimetry The DSC spectrums representing the heat flow with temperature for the charged cathode are presented as Fig.9. The figure shows that the cathodes of cells charged to 3.85 and 3.95V have no thermal peaks in the low temperature region whereas the cells charged to 4.20 and 4.35V have well defined exothermic peaks of the order of 4.9 and 7.0 J g respectively below 100 C. Even though the intensity of these peaks is low they arouse more curiosity as no such peaks in this temperature region have so far been reported. In MacNeil and Dahn 2001 the authors made in-depth thermal study of the cathode .